Interproximal reduction treatment planning

ABSTRACT

Systems and methods are disclosed for displaying a digital model of a patient&#39;s teeth by determining interproximal information associated with each tooth; and annotating a graphical representation of the model of the tooth to provide a visual display of the interproximal information.

BACKGROUND

The orthodontics industry is continuously developing new techniques forstraightening teeth that are more comfortable and less detectable thantraditional braces. One such technique has been the development ofdisposable and removable retainer-type appliances. As each appliance isreplaced with the next, the teeth move a small amount until they reachthe final alignment prescribed by the orthodontist or dentist. Thissequence of dental aligners is currently marketed as the Invisalign®System by Align Technology, Inc., Santa Clara, Calif.

One problem experienced during treatment is a residual crowding ofadjacent teeth due to insufficient interproximal reduction (IPR). Thisresidual crowding can impede complete tooth alignment, and generallynecessitates further abrasion reduction. Another problem is theoccurrence of residual spaces between adjacent teeth due to excessiveIPR. IPR represents a total amount of overlap between two teeth during acourse of treatment. Such overlap must be treated by the clinician byremoving material from the surface of the tooth. During the IPRprocedure, a small amount of enamel thickness on the surfaces of theteeth is removed to reduce the mesiodistal width and space requirementsfor the tooth. The IPR procedure is also referred to as stripping,reproximation, and slenderizing. IPR is typically employed to createspace for faster/easier-orthodontic treatment.

SUMMARY

Systems and methods are disclosed for displaying a digital model of apatient's teeth by determining interproximal information associated witheach tooth; and annotating a graphical representation of the model ofthe tooth to provide a visual display of the interproximal information.

Implementations of the invention may include one or more of thefollowing. The interproximal information can be either interproximalreduction information or interproximal gap information. Theinterproximal information can include a content element and a linkelement. The content element can be a tooth identification, one or moretreatment stages, and an interproximal distance, while the link elementcan be a line drawn to an interproximal region on the model of the toothand that points to a three-dimensional area on the model of the tooth.An angle of rotation can be displayed with the graphical representationof the model of the tooth. A compass control can be associated with theangle of rotation. The computer receives a digital data set representingthe patient's teeth and uses the data set to generate one or moreorthodontic views of the patient's teeth. The system capturesthree-dimensional (3D) data associated with the patient's teeth;determines a viewpoint for the patient's teeth; applies a positionaltransformation to the 3D data based on the viewpoint; and rendering theorthodontic view of the patient's teeth based on the positionaltransformation. The system can generate a right buccal overjet view, ananterior overject view, a left buccal overjet view, a left distal molarview, a left lingual view, a lingual incisor view, a right lingual viewand a right distal molar view of the patient's teeth. A 3D graphicalrepresentation of the teeth at the positions corresponding to a selecteddata set can be rendered. Alternatively, the 3D representation can bepositioned at any arbitrary point in 3D space. The graphicalrepresentation of the teeth can be animated to provide a visual displayof the movement of the teeth along the treatment paths. Alevel-of-detail compression can be applied to the selected data set torender the graphical representation of the teeth. A human user canmodify the graphical representation of the teeth, which causesmodifications to the selected data set in response to the instructionfrom the user. A graphical interface with components representing thecontrol buttons on a video cassette recorder can be provided for a humanuser can manipulate to control the animation. A portion of the data inthe selected data set can be used to render the graphical representationof the teeth. The human user can select a tooth in the graphicalrepresentation and read information about the tooth. The information canrelate to the motion that the tooth will experience while moving alongthe treatment path. The graphical representation can render the teeth ata selected one of multiple viewing orthodontic-specific viewing angles.An input signal from a 2D input device such as a mouse or touch-screen,or alternatively a 3D gyroscopic input device controlled by a human usercan be used to alter the orientation of the teeth in the graphicalrepresentation.

Advantages of the invention include one or more of the following.Visualization is used to communicate IPR treatment information in acomputer-automated orthodontic treatment plan and appliance. Theinvention generates a realistic model of the patient's teeth withoutrequiring a user to possess in-depth knowledge of parameters associatedwith a patient dental data capture system. Additionally, expertise in 3Dsoftware and knowledge of computer architecture is no longer needed toprocess and translate the captured medical data into a realisticcomputer model rendering and animation.

The invention thus allows IPR treatment visualization to be generated ina simple and efficient manner. It also improves the way a treatingclinician performs case presentations by allowing the clinician toexpress his or her treatment plans more clearly. Another benefit is theability to visualize and interact with models and processes without theattendant danger, impracticality, or significantly greater expense thatwould be encountered in the same environment if it were physical. Thus,money and time are saved while the quality of the treatment plan isenhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary user interface of a teeth viewer withinterproximal information annotations.

FIG. 2 shows in more detail the interproximal annotation.

FIG. 3 illustrates an exemplary rotation of the teeth shown in FIG. 1

FIGS. 4A-4D show an exemplary process for providing and viewinginter-proximal information annotation.

DESCRIPTION

FIG. 1 shows an exemplary view with IPR annotations. The view isgenerated by a viewer program such as ClinCheck® software, availablefrom Align Technology, Inc. of Santa Clara, Calif. As shown therein, anexemplary IPR annotation 2 is associated through a link 4 with a modelof tooth 10. The annotation 2 indicates that there is a 0.3 mm overlapfor teeth 10 and 11 between treatment stages 4-10. A visual indicator 6is provided to indicate a current viewing position. The indicator 6 isreferred to as a compass control because it is similar in function to acompass. Each compass control is associated with an angle of rotation.As the view of the scene rotates, so do the compass controls and anycontent therein. An easy way to visualize this is to imagine the compasscontrol as an actual compass, with its north tracking the direction ofthe front teeth. In an IPR presentation, the orientation of the compasscontrol 6 is determined by a minimum angle between the sagittal plane ofthe scene and the camera vector.

The viewer program also includes an animation routine that provides aseries of images showing the positions of the teeth at each intermediatestep along the treatment path. A user such as a clinician controls theanimation routine through a VCR metaphor, which provides control buttons8 similar to those on a conventional video cassette recorder. Inparticular, the VCR metaphor includes a “play” button that, whenselected, causes the animation routine to step through all of the imagesalong the treatment path. A slide bar can be used to request movement bya predetermined distance with each successive image displayed. The VCRmetaphor also includes a “step forward” button and a “step back” button,which allow the clinician to step forward or backward through the seriesof images, one key frame or treatment step at a time, as well as a “fastforward” button and a “fast back” button, which allow the clinician tojump immediately to the final image or initial image, respectively. Theclinician also can step immediately to any image in the series by typingin the stage number.

As described in commonly owned U.S. Pat. No. 6,227,850, the content ofwhich is incorporated by reference, the viewer program receives a fixedsubset of key positions, including an initial data set and a final dataset, from the remote host. From this data, the animation routine derivesthe transformation curves required to display the teeth at theintermediate treatment steps, using any of a variety of mathematicaltechniques. One technique is by invoking the path-generation programdescribed above. In this situation, the viewer program includes thepath-generation program code. The animation routine invokes this codeeither when the downloaded key positions are first received or when theuser invokes the animation routine.

FIG. 2 shows a single IPR annotation 2 in more detail. For each IPRvalue there are two display components. The first is a content elementon the compass control. This content element is placed on the compasscontrol with an angle corresponding to the angle between the IPR regionand the sagittal plane discussed above. The content consists of the IPRamount in millimeters, the stages during which the overlap occurs, andthe tooth ID's for the adjacent teeth.

The second display element is a link element 4 shown in FIG. 1. In oneembodiment, the link element is a line drawn from a 2D screen positionadjacent to the first content element to the point in 3D spacecorresponding to the IPR region. This line is drawn in a later renderingpass than the rest of the scene. This ensures than no part of the scenecan obscure the line. Whenever the camera is repositioned, a series ofcalculations are performed before the scene is redrawn. They occur in anundefined order.

The angle between the sagittal plane and the camera is recalculated sothat the compass control may show its proper orientation. When thecamera is moved, the 2D to 3D line is ‘dirtied’ in a rendering sense.When it is therefore re-rendered, then and only then is the calculationperformed to determine the 2D point. In addition to this dirtyingoperation, the pixel offsets for the compass control display elementsare recalculated when the camera position is changed. The 3D scenecoordinate is fixed and does not need to be recalculated. FIG. 3 showsthe IPR presentation when a scene is rotated.

The viewer program displays an initial image of the teeth and, ifrequested by the clinician, a final image of the teeth as they willappear after treatment. The clinician can rotate the images in threedimensions to view the various tooth surfaces, and the clinician cansnap the image to any of several predefined viewing angles. Theseviewing angles include the standard front, back, top, bottom and sideviews, as well as orthodontic-specific viewing angles, such as thelingual, buccal, facial, occlusal, and incisal views. The viewer programallows the clinician to alter the rendered image by manipulating theimage graphically. For example, the clinician can reposition anindividual tooth by using a mouse to click and drag or rotate the toothto a desired position. In some implementations, repositioning anindividual tooth alters only the rendered image; in otherimplementations, repositioning a tooth in this manner modifies theunderlying data set. In the latter situation, the viewer programperforms collision detection to determine whether the attemptedalteration is valid and, if not, notifies the clinician immediately.Alternatively, the viewer program modifies the underlying data set andthen uploads the altered data set to the remote host, which performs thecollision detection algorithm. The clinician also can provide textualfeedback to the remote host through a dialog box in the interfacedisplay. Text entered into the dialog box is stored as a text object andlater uploaded to the remote host or, alternatively, is delivered to theremote host immediately via an existing connection.

The viewer program optionally allows the clinician to isolate the imageof a particular tooth and view the tooth apart from the other teeth. Theclinician also can change the color of an individual tooth or group ofteeth in a single rendered image or across the series of images. Thesefeatures give the clinician a better understanding of the behavior ofindividual teeth during the course of treatment. Another feature of theviewer program allows the clinician to receive information about aspecific tooth or a specific part of the model upon command, e.g., byselecting the area of interest with a mouse. The types of informationavailable include tooth type, distance between adjacent teeth, andforces (magnitudes and directions) exerted on the teeth by the aligneror by other teeth. Finite element analysis techniques are used tocalculate the forces exerted on the teeth. The clinician also canrequest graphical displays of certain information, such as a plot of theforces exerted on a tooth throughout the course of treatment or a chartshowing the movements that a tooth will make between steps on thetreatment path. The viewer program also optionally includes “virtualcalipers,” a graphical tool that allows the clinician to select twopoints on the rendered image and receive a display indicating thedistance between the points.

FIG. 4A shows an exemplary process for providing IPR informationannotation. When the user enables IPR annotation viewing orpresentation, a compass control is create (30). Next, for each IPR value(32), the process generates the text for the IPR (34). The process alsodetermines the angle off of the sagittal plane of the IPR (36). The textand angle information is added to the compass control as a displayelement (38). In 38, the adding of a display element to the compasscontrol triggers the sub-process of recalculating the pixel offsets foreach display element. Other events that triggers such a recalculation ischanging the current angle of the compass control, as indicated with theoff page reference, or a resizing of the control, among others. Anobject is also added to the 3D scene which will draw a line from atarget point to the display element (40). Next, the process checkswhether additional IPR data needs to be processed (42). If more IPR dataremains, the process loops back to 32, and otherwise the process exits.

Turning now to FIG. 4B, from 38 (FIG. 4A), the process regenerates thecompass control offsets (50). For each entry, the process calculates andstores the size of the display elements (52). Next, the process findsthe display element closes to the current direction of the compass (54).The entry is assigned the ideal offset in pixels (56).

The compass control is associated with a number of static displayelements, each of which is associated with 2 values: a size value(relating to the text width) and a display angle value. During therecalculation of pixel offsets, the compass control determines the firstthe ideal pixel offset from the center of the control for the center ofthe display element. For instance, if the angle of the compass was 180degrees, and the compass control was trying to render a display elementat 180 degrees, the ideal pixel offset is 0 because the display elementshould be perfectly centered. If the compass is at 185 degrees, then thepixel offset is going to be a small number indicating that the displayelement should be drawn left of the center. When only one displayelement is on a compass this is all the calculation that needs to occur.However, if there is more than one element, it is possible that thedisplay elements would overlap if both drawn at their ideal offsets.Therefore, starting with the centermost display element, that is, theone with the smallest absolute value for its ideal pixel offset, eachdisplay element has its pixel offset increased (or decreased dependingon direction) until the overlap does not occur. Once all calculationsare done, the pixel offsets are stored with each display element. Theyare then referenced when the compass control is rendering itself so thateach display element can be placed.

For each entry left of the middle most entry up to the current compassdirection and π (58), the process calculates and stores the ideal offsetin pixels (60). The process checks whether the display elements overlapsthe previous entry (62). If so, the process shifts the offset left untilthe overlap disappears (64). From (62) or (64), the process checkswhether additional display elements are left of the ideal offset (66).If so, the process loops back to 58. Otherwise, the process continues onfor each entry right of the middle most entry up to the current compassdirection—π (68), the process calculates and stores the ideal offset inpixels (70). The process checks whether the display elements overlapsthe previous entry (72). If so, the process shifts the offset left untilthe overlap disappears (74). From (72) or (74), the process checkswhether additional display elements are right of the ideal offset (76).If so, the process loops back to 68. Otherwise, the process exits.

Turning now to FIG. 4C, an exemplary process to render compass controlis shown. First, the process determines a control size in pixels (82).Next, background tick marks are drawn (84). For each display element(86), the process checks if the display element is in a renderable area(88). If so, the display element is rendered at the pre-calculatedoffset (90). From 88 or 90, the process checks whether additionaldisplay elements remain (92). If so, the process loops back to 86 andotherwise the process exits.

Referring now to FIG. 4D, an exemplary process for user navigation withthe 3D scene is shown. First, the view updates camera position (102).This triggers two parallel forks. In the first fork, the compass controlcalculates and stores the angle between the sagittal plane and thecamera position (104). Next, the compass control redraws itself usingthe newly determined angle (106). Further, the compass controlrecalculates off-sets using the new angle by jumping to 50 (FIG. 4B). Inthe second fork, the 3D line element sets itself as ‘dirty’ in order forthe line element to be rendered (110).

In 112, all call-backs are completed, and the viewer begins rendering a3D view (114). For each 3D line object (116), the process determinesorigin by determining position of the IPR in the scene (118). Theprocess also computes the destination by retrieving the offset positionof the IPR display element in the compass control (120). Next, theprocess checks whether the destination is on the screen (122). If so, itrenders the line. From 122 or 124, the process checks whether additional3D line objects remain (126). If so, it loops back to 116 and if not,the process exits.

At some point after the compass control recalculates its offsets, thewindows control will be re-rendered. Since the control is a windowscontrol and not a 3D rendering context, its rendering is not tied to therendering of the 3D view, though in practice the mechanisms that causeone to re-render will also indirectly trigger a re-render of the other.

A simplified block diagram of a data processing system that may be usedto develop orthodontic treatment plans is discussed next. The dataprocessing system typically includes at least one processor whichcommunicates with a number of peripheral devices via bus subsystem.These peripheral devices typically include a storage subsystem (memorysubsystem and file storage subsystem), a set of user interface input andoutput devices, and an interface to outside networks, including thepublic switched telephone network. This interface is shown schematicallyas “Modems and Network Interface” block, and is coupled to correspondinginterface devices in other data processing systems via communicationnetwork interface. Data processing system could be a terminal or alow-end personal computer or a high-end personal computer, workstationor mainframe.

The user interface input devices typically include a keyboard and mayfurther include a pointing device and a scanner. The pointing device maybe an indirect pointing device such as a mouse, trackball, touchpad, orgraphics tablet, or a direct pointing device such as a touch-screenincorporated into the display, or a three dimensional pointing device,such as the gyroscopic pointing device described in U.S. Pat. No.5,440,326, other types of user interface input devices, such as voicerecognition systems, can also be used.

User interface output devices typically include a printer and a displaysubsystem, which includes a display controller and a display devicecoupled to the controller. The display device may be a cathode ray tube(CRT), a flat-panel device such as a liquid crystal display (LCD), or aprojection device. The display subsystem may also provide non-visualdisplay such as audio output.

Storage subsystem maintains the basic required programming and dataconstructs. The program modules discussed above are typically stored instorage subsystem. Storage subsystem typically comprises memorysubsystem and file storage subsystem.

Memory subsystem typically includes a number of memories including amain random access memory (RAM) for storage of instructions and dataduring program execution and a read only memory (ROM) in which fixedinstructions are stored. In the case of Macintosh-compatible personalcomputers the ROM would include portions of the operating system; in thecase of IBM-compatible personal computers, this would include the BIOS(basic input/output system).

File storage subsystem provides persistent (non-volatile) storage forprogram and data files, and typically includes at least one hard diskdrive and at least one floppy disk drive (with associated removablemedia). There may also be other devices such as a CD-ROM drive andoptical drives (all with their associated removable media).Additionally, the system may include drives of the type with removablemedia cartridges. The removable media cartridges may, for example behard disk cartridges, such as those marketed by Syquest and others, andflexible disk cartridges, such as those marketed by Iomega. One or moreof the drives may be located at a remote location, such as in a serveron a local area network or at a site on the Internet's World Wide Web.

In this context, the term-“bus subsystem” is used generically so as toinclude any mechanism for letting the various components and subsystemscommunicate with each other as intended. With the exception of the inputdevices and the display, the other components need not be at the samephysical location. Thus, for example, portions of the file storagesystem could be connected via various local-area or wide-area networkmedia, including telephone lines. Similarly, the input devices anddisplay need not be at the same location as the processor, although itis anticipated that personal computers and workstations typically willbe used.

Bus subsystem is shown schematically as a single bus, but a typicalsystem has a number of buses such as a local bus and one or moreexpansion buses (e.g., ADB, SCSI, ISA, EISA, MCA, NuBus, or PCI), aswell as serial and parallel ports. Network connections are usuallyestablished through a device such as a network adapter on one of theseexpansion buses or a modem on a serial port. The client computer may bea desktop system or a portable system.

Scanner is responsible for scanning casts of the patient's teethobtained either from the patient or from an orthodontist and providingthe scanned digital data set information to data processing system forfurther processing. In a distributed environment, scanner may be locatedat a remote location and communicate scanned digital data setinformation to data processing system via network interface.

Fabrication machine fabricates dental appliances based on intermediateand final data set information received from data processing system. Ina distributed environment, fabrication machine may be located at aremote location and receive data set information from data processingsystem via network interface.

The invention has been described in terms of particular embodiments.Other embodiments are within the scope of the following claims. Forexample, the system can show IPRs as well as interproximal gaps, orspaces that appear between adjacent teeth in the dental arches.

1. A method for displaying a digital model of a patient's teeth, comprising: determining interproximal information associated with each tooth; and annotating a graphical representation of the model of the tooth to provide a visual display of the interproximal information.
 2. The method of claim 1, wherein the interproximal information comprises interproximal reduction information or interproximal gap information.
 3. The method of claim 1, wherein the interproximal information comprises a content element and a link element.
 4. The method of claim 3, wherein the content element comprises of a tooth identification, one or more treatment stages, and an interproximal distance.
 5. The method of claim 3, wherein the link element comprises a line drawn to an interproximal region on the model of the tooth.
 6. The method of claim 1, wherein the line points to a three-dimensional area on the model of the tooth.
 7. The method of claim 1, comprising displaying an angle of rotation with the graphical representation of the model of the tooth.
 8. The method of claim 7, comprising displaying a compass control associated with the angle of rotation.
 9. The method of claim 1, comprising determining a treatment path for each tooth; and updating the graphical representation of the teeth to provide a visual display of the position of the teeth along the treatment paths.
 10. The method of claim 1, comprising: determining a viewpoint for the teeth model; applying a positional transformation to the 3D data based on the viewpoint; and rendering a graphical representation of the teeth model based on the positional transformation.
 11. The method of claim 1, comprising generating one of: a right buccal overjet view of the patient's teeth, an anterior overject view of the patient's teeth, a left buccal overjet view of the patient's teeth, a left distal molar view of the patient's teeth, a left lingual view of the patient's teeth, a lingual incisor view of the patient's teeth, a right lingual view of the patient's teeth, and a right distal molar view of the patient's teeth.
 12. The method of claim 1, comprising rendering a 3D graphical representation of the teeth at the positions corresponding to a selected data set.
 13. The method of claim 1, comprising receiving an instruction from a human user to modify the graphical representation of the teeth.
 14. The method of claim 13, comprising modifying the selected data set in response to the instruction from the user.
 15. The method of claim 1, comprising providing a graphical interface, with components representing the control buttons on a video cassette recorder, which a human user can manipulate to control the animation.
 16. The method of claim 1, comprising allowing a human user to select a tooth in the graphical representation and, in response, displaying information about the tooth.
 17. The method of claim 16, wherein the information relates to the motion that the tooth will experience while moving along the treatment path.
 18. The method of claim 1, comprising rendering the teeth at a selected one of multiple viewing orthodontic-specific viewing angles.
 19. The method of claim 1, comprising receiving an input signal from a 3D gyroscopic input device controlled by a human user and using the input signal to alter the orientation of the teeth in the graphical representation.
 20. A system for displaying a digital model of a patient's teeth, comprising: means for determining interproximal information associated with each tooth; and means for annotating a graphical representation of the model of the tooth to provide a visual display of the interproximal information. 